Terminal Log Error,critical

hello,
when i login to mikroik terminal i see this
echo: system,error,critical login failure for user Administrator from 218.104.145.18 via ftp
every 2 sec , how can i stop this
also have DNS DOS attack on my dns server , low incoming traffic but high outgouing traffic , so it completely down users internet
i tried to block src ip but they change every day …
any suggestion
Thanks

Try this.

http://wiki.mikrotik.com/wiki/Bruteforce_login_prevention